HEAT TRANSFER INVESTIGATION OF THE SUB- AND SUPERCRITICAL FUEL FLOW THROUGH A U-TURN TUBE

摘要

This paper was to experimentally study the heat transfer characteristics within an air/fuel heat exchanger in an attempt to cool the cooling air from the compressor with RP-3 kerosene as the coolant and at the same time heat it up over its critical temperature. The supercritical fuel was then injected into the combustor while the cooled cooling air was led to the turbine for blade and disk cooling. In the experiments, a series of vertical U-turn tubes were heated from outside and the RP-3 flowed through them at supercritical pressures s (p_(red) ～ 2). The test section heat flux, inlet Reynolds number and the dimensionless bend diameter BD/d were three main influencing factors under consideration. Test results indicated that the Nusselt number increased with heat flux if the reduced bulk fuel temperature T_b/T_c was lower than 1.179 (760K). In addition, heat transfer was enhanced when the fuel temperature near its critical point for all experimental runs, and in the bend regions, the heat transfer was enhanced due to the strong secondary flow induced by the centrifugal force and however, the enhancement was not obvious for low Reynolds number cases. From the test results, a correlation was developed which predicted the heat transfer for RP-3 fairly well.